QProcess/Unix: fix close() on invalid file descriptor

Commit 90bc0ad41f9937f9cba801b3166635f6f55e0678 ("QProcess/Unix: add
failChildProcessModifier()") added this line that set childStartedPipe
so that the failChildProcess() callback had something to write to. But
we left it set on exit from QProcessPrivate::startDetached(), which
caused the QProcess destructor to try and close it.

Noticed when debugging the issue for QTBUG-123083.

Task-number: QTBUG-123083
Change-Id: I6818d78a57394e37857bfffd17bbc41c8400270f
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit 0f56502fb6f062c6d2308198c93412c34525125b)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit a2d67a2671f8b2ab96d4b458d80972c2bd83b3db)

2 files changed, 22 insertions, 6 deletions

diff --git a/src/corelib/io/qprocess_unix.cpp b/src/corelib/io/qprocess_unix.cpp
index ca65a3c776..fcbce92ade 100644
--- a/src/corelib/io/qprocess_unix.cpp
+++ b/src/corelib/io/qprocess_unix.cpp
@@ -1290,7 +1290,6 @@ void QProcessPrivate::waitForDeadChild()
 bool QProcessPrivate::startDetached(qint64 *pid)
 {
     AutoPipe startedPipe, pidPipe;
-    childStartedPipe[1] = startedPipe[1];
     if (!startedPipe || !pidPipe) {
         setErrorAndEmit(QProcess::FailedToStart, "pipe: "_L1 + qt_error_string(errno));
         return false;
@@ -1309,6 +1308,7 @@ bool QProcessPrivate::startDetached(qint64 *pid)
         return false;
     }
 
+    childStartedPipe[1] = startedPipe[1];   // for failChildProcess()
     pid_t childPid = childProcess.doFork([&] {
         ::setsid();
 
@@ -1323,6 +1323,7 @@ bool QProcessPrivate::startDetached(qint64 *pid)
         qt_safe_write(pidPipe[1], &doubleForkPid, sizeof(pid_t));
         return 0;
     });
+    childStartedPipe[1] = -1;
 
     int savedErrno = errno;
     closeChannels();
diff --git a/tests/auto/corelib/io/qprocess/tst_qprocess.cpp b/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
index 46c25b9067..1056eaa107 100644
--- a/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
+++ b/tests/auto/corelib/io/qprocess/tst_qprocess.cpp
@@ -1488,6 +1488,9 @@ struct DisableCrashLogger
     }
 };
 
+QT_BEGIN_NAMESPACE
+Q_AUTOTEST_EXPORT bool _qprocessUsingVfork() noexcept;
+QT_END_NAMESPACE
 static constexpr char messageFromChildProcess[] = "Message from the child process";
 static_assert(std::char_traits<char>::length(messageFromChildProcess) <= PIPE_BUF);
 static void childProcessModifier(int fd)
@@ -1499,17 +1502,28 @@ static void childProcessModifier(int fd)
 void tst_QProcess::setChildProcessModifier_data()
 {
     QTest::addColumn<bool>("detached");
-    QTest::newRow("normal") << false;
-    QTest::newRow("detached") << true;
+    QTest::addColumn<bool>("useVfork");
+    QTest::newRow("normal") << false << false;
+    QTest::newRow("detached") << true << false;
+
+#ifdef QT_BUILD_INTERNAL
+    if (_qprocessUsingVfork()) {
+        QTest::newRow("normal-vfork") << false << true;
+        QTest::newRow("detached-vfork") << true << true;
+    }
+#endif
 }
 
 void tst_QProcess::setChildProcessModifier()
 {
     QFETCH(bool, detached);
+    QFETCH(bool, useVfork);
     int pipes[2] = { -1 , -1 };
     QVERIFY(qt_safe_pipe(pipes) == 0);
 
     QProcess process;
+    if (useVfork)
+        process.setUnixProcessParameters(QProcess::UnixProcessFlag::UseVFork);
     process.setChildProcessModifier([pipes]() {
         ::childProcessModifier(pipes[1]);
     });
@@ -1542,7 +1556,11 @@ void tst_QProcess::failChildProcessModifier()
             "Implementation detail: the length of the message is limited");
 
     QFETCH(bool, detached);
+    QFETCH(bool, useVfork);
+
     QProcess process;
+    if (useVfork)
+        process.setUnixProcessParameters(QProcess::UnixProcessFlag::UseVFork);
     process.setChildProcessModifier([&process]() {
         process.failChildProcessModifier(failureMsg, EPERM);
     });
@@ -1651,9 +1669,6 @@ void tst_QProcess::terminateInChildProcessModifier()
 #endif
 }
 
-QT_BEGIN_NAMESPACE
-Q_AUTOTEST_EXPORT bool _qprocessUsingVfork() noexcept;
-QT_END_NAMESPACE
 void tst_QProcess::raiseInChildProcessModifier()
 {
 #ifdef QT_BUILD_INTERNAL